The present invention relates to a device and a method for detecting loss of pneumatic pressures in the tires set on a vehicle. More particularly, the invention relates to a device and a method for accurately detecting loss of pneumatic pressures in the tires by detecting that the kinds of the tires set on a vehicle are different.
When pneumatic pressure of the tires set on a vehicle is lowered, fuel cost is aggravated, and danger for bursting is invited in high velocity running. Conventionally, loss of pneumatic pressure of tire is detected by utilizing the change in the characteristics of the tire such as decrease in the dynamic loaded radius of the tire or variation in the resonance frequency resulting from the loss of pressure.
For example, conventional device for detecting loss of pneumatic pressure in tire utilizes a principle that when a specified tire of a certain vehicle shows loss of pressure, the outer diameter (dynamic loaded radius of tire) of such tire decreases more than that of the tire having normal internal pressure, so that its rotational angular velocity shows increase more than that of the other normal type. For example, according to the method of detecting loss of internal pressure from the comparative differences in the rotational angular velocity, the following expression is used as an identification value (Japanese Unexamined Patent Publication No. 63-305011):DEL={(F1+F4)/2−(F2+F3)/2}/{(F1+F2+F3+F4)/4}×100 (%)wherein F1 to F4 denote the rotational angular velocities of front left tire, front right tire, rear left tire and rear right tire, respectively.
However, in case of the difference in the kinds of the set tires, no accurate detection of the pneumatic pressure of the tire can be expected.
To meet the situation, there have been proposed the methods for finding abrasion of the tire and identifying the kind of the tire.
The invention of Japanese Unexamined Patent Publication No. 9-188114 discloses a method for identifying whether the kind of the tires set on the vehicle is, for example, the summer use or winter use, by comparing the inclination of a straight line at the time of plotting the ratio between the rotational velocity of the front wheel and the rotational velocity of the rear wheel to the vehicle velocity with the previously calibrated data of the tires of the known kinds.
The invention of Japanese Unexamined Patent Publication No. 11-78442 uses a relationship of the ratio between the rotational velocity of the front wheels and the rotational velocity of the rear wheels with the acceleration rate of the vehicle, so as to detect the abrasive condition of the tire.
The invention of Japanese Unexamined Patent Publication No. 2000-79812 discloses a method for identifying whether the tires set on the driving shaft are for summer use or for winter use by utilizing the inverse of the rotary radius by using the tire pressure decrease identification value (DEL), but said method is limited to the application to a vehicle furnished with LSD (Limited slip differential).
Japanese Unexamined Patent Publication No. 2002-19435 Publication and Japanese Unexamined Patent No. 2002-181669 use the relationship between the slip ratio (a value obtained by dividing the difference between the rotational velocity of the following wheel and the rotational velocity of the driving wheel by the rotational velocity of the driving wheel) so as to identify the kind of the tire.
Japanese Unexamined Patent Publication No. 2002-211220 discloses a method for identifying the kind of the tire by the size of spreading of the identification values of pressure decrease of tire (average of the absolute values of the identification values of pressure decrease of tire).
Besides, there is a method for changing the tire identification method in the case where the wheels have different rotational characteristics due to the difference of the tire characteristics on computation of the standard values from the angular velocity of the wheels based on each velocity interval of vehicles (German PAO 10300330 Specification No. 10300330).
In the case where the different kinds of tires are used depending on the position of setting on the vehicle, especially when the kinds of the tires set on each of the right and left driving wheels are different, decrease in the tire pressures cannot accurately be identified with the threshold value for identifying the pressure decrease of tires having the same kind of tires set. Furthermore, when the kinds of the tires set on the respective ones of the right and left driving wheels are different, because of the difference of the driving characteristics between the right and the left sides, problems occur such that slips occur and brake operations do not work smoothly to cause elongation of the brake distance, and so on. Consequently, it becomes necessary to give warning to the driver that the kinds of the tires are different between the right and left driving wheels respectively, or to make the wheel control device (such as ABS, TRC) operative to meet the different kinds of the tires.